Considering prior art mounting arrangements for a spinning rotor, Czechoslovak Patent Specification No. 140 257 discloses an arrangement wherein the shaft, on which the spinning rotor is mounted, passes through a recess in a supporting sleeve and, at its end, is fixed in its conical fastening surface at the start of the supporting sleeve, or over the whole length of the recess there being disposed a resilient element. At the external side of the supporting sleeve at its ends, there are located ball bearings which are directly fixed within the recess of the spinning housing. Thus, the shaft is, in essence, constituted by a dynamically elastic portion, which, through its fastening surface, is fixed in the dynamically rigid portion constituted by the supporting sleeve. Relative to the fixation of the conical fastening surface within the bearing arrangement at the end of the supporting sleeve, the dynamically elastic portion is provided with a resilient element at the opposite end of the supporting sleeve. This design is rather complex and exacting not only from manufacturing point of view, but in operation, the resilient element will show, after a certain time, a decrease in elasticity thereby resulting in higher vibration amplitudes of the rotor. The forces from the vibrating shaft are transmitted directly into the bearings thereby causing considerable noise.
These have been the reasons for the development of a special mounting arrangement disclosed, for example, in Czechoslovak Patent Specification No. 181 015, wherein, on the one hand, the spindle comprises an outer sleeve with races for two ball rows arranged in cages, a shaft provided with races, whose external end portion is adapted for power transmission from the driving means and whose internal end portion is adapted for mounting arrangement of the spinning rotor, as well as a seal for sealing the annular gap, and, on the other hand, a resilient-mounted intermediate sleeve for fixing the outer sleeve provided with an internal wall and resilient damping elements with an outer supporting sleeve for mounting within the spinning housing. With this design, however, the shaft constitutes a dynamically rigid portion, through which forces from the vibrating rotor are directly transmitted into both ball rows. Further, this approach is also inadequate for high rotor speeds up to 90,000 revolutions per minute and higher, as it is not capable of damping the vibrations of the rotor. Although a relatively accurate balanced state of the rotor during its manufacture is achieved, in operation, an uneven deposition of dirt or other impurities upon the so-called collecting groove in the rotor takes place, thus disturbing the balanced state of the rotor and causing vibrations which promote rapid wear of the races and balls. At the same time, the noise produced greatly exceeds admissible limits. The operation speeds approach critical speeds of the third degree, and substantial dynamic forces act upon the race-ball complement or assembly thereby reducing the reliability and service-life of the whole spindle to an intolerable degree, and thus making the spindle unsuitable for use at the speeds mentioned.
With respect to sealing of the compensation space between the spinning rotor and the front wall of the outer sleeve, it is known, for example, from Czechoslovak Patent Specification No. 181 015, to provide a labyrinth seal constituted by a labyrinth knife or blade arranged directly on the spinning rotor hub. The labyrinth knife is oriented towards the wall of the spinning housing. With respect to the resilient mounting of the outer sleeve with the rigid shaft within the intermediate sleeve with resilient damping elements, the rotor, due to the imbalance thereof, is caused to vibrate thereby causing contact of the labyrinth knife with the wall of the spinning housing. Therefore, it has been necessary to select greater clearance values between the labyrinth knife and the spinning housing, which has resulted in a reduction in the efficiency of the seal and this again unfavorably affects pneumatic conditions within the rotor space of the spinning housing where for technological reasons concerning the fibre supply there is sub-atmospheric pressure generated through exhaustion of air from the spinning rotor.
In Czechoslovak Patent Specification No. 238 202, a labyrinth seal construction is disclosed wherein the labyrinth gap is created between the external labyrinth surface provided on the spinning rotor-hub and the internal wall of the cylindrical shaped orifice within the intermediate sleeve with resilient damping elements. Because the relatively rigid shaft guided in the outer sleeve will not allow higher vibration excitation relative to the intermediate sleeve, and because the rotor unbalance-related vibrations are dampened solely by damping elements arranged on the intermediate sleeve, the seal is sufficient for use over a certain speed range. However, the seal provides insufficient damping of the rotor vibrations causing, on the one hand, premature wear, and, on the other hand, excessive noise. These limitations manifest themselves especially at speeds of 90,000 revolutions per minute and above.